The agent 99MTC hexamethylpropyldeneamineoxime (99MTC HM- PAO) has been proposed as a cerebral blood flow (CBF) traces for use in humans using single photon emission tomography (SPECT). The mechanism of the binding of this agent is not well understoood, nor has the use of this compound been shown to yield absolute quantitative cerebral blood flow data. In this proposal we wish to study the dynamics of this compound in the blood and in cerebral tissue as that we may understand it's limitations as a tracer for the quantitative measurement of cerebral blood flow. We will determine the relationship between the distribution of 99MTC HM-PAO and CBF as measured with a standard CBF tracer, 14C iodoantipyrine. The studies will be undertaken in animals using quantitative double label autoradiography under a variety of conditions to ascertain when this tracer can be used as a quantitative indicator of CBF. This agent has potential use in the study of many pathological conditions, both in animal models using autoradiography and in humans using SPECT. If we find that 99MTC HM-PAO is not completely trapped in the tissue then we will examine other mathematical models in order to describe the behavior of 99MTC HM-PAO. Having characterized the fate of HM-PAO under normal conditions it's usefulness as a CBF agent in human pathology will be evaluated in animal models of stroke (acute and chronic), epilepsy and flow-metabolism uncoupling (ibotenic acid lesions).